There has been known a cooling method in which outside cool air is taken into an apparatus using a fan to cool electronic devices and electronic components inside, and warm air produced along with the cooling is exhausted to the outside of the apparatus. As for such a cooling method, there has been known a technique of providing a shutter to an apparatus to inhibit the exhausted warm air from flowing back into the apparatus when the fan stops. Examples of such known techniques include providing a check valve which is opened by the intake and exhaust by the fan and closed when the fan stops, and providing a flap which turns by receiving air pressure of a countercurrent air flow produced when the fan stops, and closes the flow passage.
For an air-pressure type shutter which opens by the intake and exhaust by a fan, when the rotation speed of the fan decreases and the amount of air flow decreases, it is possible that the shutter does not open in some cases. If the shutter does not open, the efficiency of cooling heat generating objects in the apparatus, such as electronic devices and electronic components, goes down, and it is possible to cause the performance deterioration and failure.
The followings are reference documents.    [Document 1] Japanese Laid-open Patent Publication No. 2012-190222 and    [Document 2] Japanese Laid-open Patent Publication No. 2011-231954.